A sinkhole the size of a backyard swimming pool has opened up in a street near Australian Prime Minister Malcolm Turnbull's Sydney harbourside mansion.

A gas line ruptured on Wentworth Street in Point Piper when a large part of the footpath collapsed and washed away today after about half a month's worth of rain pelted the city yesterday.

Rainwater could be seen streaming into the sinkhole, undercutting the earth underneath the road at the edge of the hole, which is a block away from Turnbull's home.

As emergency crews worked to limit the spread of the crater, local resident Kirsty Mirzikinian and her personal trainer watched in disbelief.

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Mirzikinian, whose home is opposite the sinkhole, told reporters she was in shock.

"My personal trainer has come, my electricity is off and now I don't know what to do," Mirzikinian said. "I can't believe there's a hole just right across the street from my house, this doesn't normally happen."

Mirzikinian said she smelt a gas leak yesterday. "We did smell a gas leak in the afternoon and the guys came and they were banging around, breaking down the concrete," she said. "Basically we woke up and it was like this."

- AAP